This invention relates to a cigarette manufacturing machine.
As is well known, cigarette manufacturing machines normally comprise a tobacco distributor, i.e. a unit the purpose of which is to transform a mass of shredded tobacco into a substantially constant continuous stream of separate tobacco particles, by successive processing stages. This stream of tobacco particles is fed either directly or by means of a belt conveyor to the lower end of a duct normally disposed in a vertical position. The upper end of said vertical duct is normally closed by a suction conveyor belt which connects the distributor to a final section of the manufacturing machine, and extends beyond the mouth of said vertical duct to reach a position, defined as the discharge position, disposed where the suction conveyor meets the feed track for a cigarette paper web.
Under the thrust of a rising air current, the tobacco particles constituting the stream generated by the distributor rise up the vertical duct and adhere to the suction conveyor belt, to form a layer or filler thereon by accumulation. The effect of the suction causes this filler to be retained by the suction belt, which transfers it from the mouth of the vertical duct to said discharge position, at which it is deposited on to the cigarette paper web.
Over that portion of its path between the vertical duct and the discharge position, the tobacco filler is subjected to a trimmer device, the purpose of which is to make its thickness substantially uniform.
From British Pat. No. 961,139 it is known to use a distributor comprising a funnel-shaped chamber or hopper for accumulating a mass of tobacco, which is defined at one end by a fixed inclined wall and at the other end by a carding unit having two rollers, known respectively as the carding and brushing rollers, and provided with teeth. These rollers rotate in the same direction substantially tangential to each other. The carding roller has a direction of rotation such as to withdraw the tobacco from the inside of the hopper in order to transfer it to the outside thereof downstream of the zone of tangency or interaction with the brushing roller. The purpose of the brushing roller is to reduce the tobacco transferred to the outside of the hopper by the carding roller, to a substantially uniform layer which is fed in known manner to the vertical duct in the form of a continuous and substantially uniform stream of tobacco particles.
A chamber for containing a mass of shredded tobacco is disposed above the funnel-shaped hopper and the carding unit. The chamber is bounded at the bottom by a conveyor belt, and on two sides by a fixed wall and an elevator belt consisting of the rising run of an endless belt. By means of teeth or blades fitted to its surface, the elevator belt withdraws tobacco from the inside the chamber, and deposits it, by means of its descending run, into said funnel-shaped chamber. During this transfer, the tobacco is subjected to a preliminary carding operation by two toothed rollers cooperating with the elevator belt.
The critical point of the described distributor is the funnel-shaped hopper for feeding the tobacco to the carding unit. The hopper comprises a vessel of substantially constant volume bounded by fixed and mobile walls, between which a mass of tobacco remains for prolonged periods of time, during which it is subjected to a continuous turning action and to high compression. This treatment leads to the formation of tangled tobacco particles (known as knots or cords) with partial nullification of the effects of the preliminary carding operation. A further serious consequence of this treatment is that tobacco particles having different physical characteristics separate at different levels. More precisely, the longer particles from shredding of the blade part of the tobacco leaf tend to concentrate in the top of the hopper. In contrast, the shorts originating both during said shredding operation and from crumbling of the longer particles during subsequent treatment stages to which the tobacco is subjected, tend to fall gradually and accumulate in the base of the hopper. In particular, because of the prolonged compression and turning action to which the tobacco mass is subjected, the percentage of shorts in hoppers of the described type reaches extremely high values.
Because of their distribution in different layers in the hopper, the tobacco particles of different physical characteristics are neither uniformly nor continuously distributed within the stream generated by the distributor. This would lead to the production of a non-uniform tobacco filler (the result of which would be the formation of cigarettes of variable weight) if known manufacturing machines did not normally use control units, in themselves extremely complicated and costly, which by recycling part of the tobacco leaving or entering the carding unit, tend to make the tobacco stream fed to the bottom of the suction conveyor as uniform as possible.
The presence of the control units not only makes known manufacturing machines extremely complicated and costly, but also makes it necessary to extremely accurately adjust all the members of such machines, thus preventing the construction of multiple manufacturing machines, i.e. manufacturing machines comprising several forming units for the so-called tobacco rod, which have at least part of their drive mechanism in common.